High pressure mercury vapor discharge lamp with metal halide additives

ABSTRACT

A high pressure mercury vapor discharge lamp having a quartz glass discharge tube and refractory metal electrodes in an envelope containing metal halides and an inert gas as the additive fill. The discharge tube contains halides of at least three elements which have essentially similar median excitation energy which comprises dysprosium and at least two other rare earth metals. The dysprosium and the at least two other rare earth metals are present in a total amount of from 0.3 to 1.2 mg/cm of arc length which during operation of the lamp provides a saturated vapor pressure and a wall loading of between 8 and 20 W/cm2.

United States Patent 11 1 Dobrusskin et al.

1111' 3,842,307 [451 Oct. 15,1974

Larson 3131184 X HIGH PRESSURE MERCURY VAPOR 3,513,344 5 1970 DISCHARGELAMP w METAL HALIDE 3,514,659 5/1970 Gunglc ct a1. 313/229 X 3,536,94710/1970 Higashi et a1. 313/229 ADDITIVES 3,662,203 5/1972 Kuhl et al.313/184 X. [75] Inventors: Alexander Dobrusskln; Helmut Leyendecker,both of Trufkirchen, German Primary Examiner-Palmer C. Demeo y A t A FFl & F h f [73] Assignee: Patent-Treuhand-Gesellschaft fur t omey' orlrm ynn au EFQFFFEEPEEE ml), Munich. Gerrriany 22 Filed: Oct. 9, 1973[57] ABSTRACT PP N03 404,609 A high pressure mercury vapor dischargelamp having Related Application Data a quartz glass discharge tube andrefractory metal electrodes in an envelope containing metal halides and[63] 5831;32 :2 of 1972 an inert gas as the additive fill. The dischargetube contains halides of at least three elements which have [30] ForeignApplication Priority Data essentially similar median excitation energywhich comprises dysprosium and at least two other rare Feb. 11,1971Germany 2106447 earth metals The dysprosium and the at least two otherrare earth metals are present in a total amount [if] cCll 313/184,313/22Pibl31g/l2/3 offrom Q3 to L2 mg/cm ofarc length which during i 225operation of the lamp provides a saturated vapor pres- 1 o earc l sureand a wall loading of between 8 and 20 W/cm [56] References Cited UNITEDSTATES PATENTS 13 Claims, 2 Drawing Figures 3,334,261 8/1967 Butler eta1. 313/229 2 l0 n n 0 6 I1 I ll Ill PAIENIED v 3.842.307 sum 1 or 2FIG. I

PAINTED 0m 1 51924 SHEEI 2 BF 2 HIGH PRESSURE MERCURY VAPOR DISCHARGELAMP WITH METAL HALIDE ADDITIVES The present application is acontinuation application of Ser.'No. 224,708 filed Feb. 9, 1972, andabandoned with the filing of the present application.

The invention relates to a high pressure mercury vapor (HPMV) electricdischarge lamp with metal halide additives. Such lamps comprise adischarge tube of fused silica with electrodes of refractory metalprotruding into the discharge tube, spaced apart by a distance which isa multiple of the discharge tube diameter. A foil seal, each, ishermetically bonded to the electrodes. An outer envelope or jacketsurrounds the discharge tube.

It is well-known to add several elements in the form of halogencompounds to the mercury. At least one of the additives may be a rareearth metal halide. The color appearance of illuminated objects isaffected by the spectral radiation distribution of the illuminant. lnorder to obtain a lamp of good color rendering properties dysprosiumiodide and thallium iodide were added, for instance, to the mercury fill(see US. Pat. No. 3,452,238). By this means a color rendering index R ofabout 85 is attained. Briefly, the color rendering index is a measure ofthe color rendering property and shows the conformity of the colorimpression of objects illuminated by a light source, with the colorimpression of the same object when illuminated by a referenceilluminant. For further definitions of this and other terms used herein,reference is made to the [ES Lighting Handbook, published by theIlluminating Engineering Society, New York, NY.

It is an object of the present invention to provide a lamp having astill better color rendering index.

SUBJECT MATTER OF THE PRESENT INVENTION The discharge tube, besidescontaining mercury and a noble or inert gas, contains halides of atleast three elements of similar average or median excitation energy,among them at least three rare earth metals in a total amount of from0.3 to 1.2 mg/cm of arc length. The wall loading of the discharge tubeis between 8 and W/cm The selection of elements of possibly identicalmedian excitation energy is of importance to the invention. lf theelements are differently chosen, the radiation of the elements havinghigher excitation energy would be decreased in view of the presence ofelements with lower excitation energy and, consequently, the totalradiation would be less, in effect like that in the prior art.

Surprisingly, it was found that the color rendering index obtained ishigher than could be expected from a mere superposition of spectra ofthe individual components. This phenomenon might possibly be explainedby the fact that due to the addition of the partial pres- A sures, andthe thereby resulting higher total pressure,

the conditions for excitation of each individual component are improvedwhereby the continuous portion of the spectrum is increased. Thisfavorably affects both luminous efficacy and color rendering. Thus, acolor rendering index of more than 95 is obtained, which has neverbefore been achieved with the previously known lamps. This renders thelamp especially suited for il- Preferably, from the group of rare earthmetals, dysprosium, holmium and thulium should simultaneously be presentin the lamp; other rare earth metals such as erbium, europium orlutetium might be added thereto. Thallium halide, preferably thalliumiodide, and cesium halide, preferably cesium iodide are preferredfurther additives, the latter for stabilization of the discharge. Anembodiment of the lamp according to the invention is illustrated in theaccompanying figures, wherein:

FIG. 1 shows the lamp in vertical section; and

FIG. 2 the spectral distribution of radiant flux of the lamp.

A typical lamp has a cylindrical discharge tube 1 of fused silica withan inner diameter of 31 mm; the volume is cc. One electrode 2, 3, each,of Th0 activated tungsten, is provided at each end of the envelope. Theelectrodes 2 and 3 are connected to the leadin wires 6 and 7,respectvely, by means of foil seals 4 and 5. The electrode spacing ismm. Thev ends of the discharge tube are provided with a coating 8 or 9of zirconium oxide reflecting heat rays. ln vertical or inclinedoperating position of the lamp, the area of the discharge tube endcovered by coating 8 and adjacent screw base 12, is smaller than thearea of the other end of the discharge tube covered by coating 9. Thedischarge tube 1 is mounted with supports 10, 11 in an outer envelope orjacket 13 provided at one end with the screw base 12.

EXAMPLE 1 The discharge tube is filled with: Ar of 30 Torr; 80 mg Hg; 12mg Tll; 3 mg Csl (the Csl being useful to stabilize the are); 25 mg Hgl3 mg Tm; 3 mg Ho; and 3 mg Dy. The latter three rare earth elementsreact with the Hgl (probably disassociated) in the discharge vessel uponbeing heated, so that the discharge vessel will contain the desiredamounts of mercury and the iodides of thulium, holmium and dysprosium.The'design data and the fill quantities apply to a lamp with a wattageinput of 3.5 kW, operated with 18 amps. and from a voltage of 380 V. Theluminous flux is 325000 lumens, the luminous efficacy 93 lm/W. Thecorrelated color temperature is 6000 K, the color rendering index R is95.

EXAMPLE 2 Wattage input of the lamp 250 W; the discharge tube has aninner diameter of 14 mm and a volume of 5.3 cc; and an electrode spacingof 25 mm. The fill in the lamp is Ar of 30 Torr, 10 mg Hg, 1 mg Csl, 12mg Hgl and 1 mg Tm, 1 mg Ho, 1 mg Dy. Upon heating, the Tm, I-lo ad Dyreact with the mercury iodide in the discharge vessel so that thedischarge vessel will have the desired amounts of mercury and theiodides of thulium, holmium and dysprosium.

EXAMPLE 3 Lamp dimensions and power as in Example 2; fill within thedischarge vessel: Ar of 30 Torr; 8 mg Hg; 1 mg Csl; 16 mg Hgl and 1 mgDy; 1 mg Tm; 1 mg Eu; 1 mg Ho; the Dy, Tin, Eu, and Ho react with theHgl as the discharge vessel is heated.

FIG. 2 shows the spectral radiant flux distribution standardized to aluminous flux of 1000 lumens of a 3.5 kW lamp in comparison withdaylight D 55 having a color temperature of 5500 K. The figure revealshow well the spectral energy distribution of the inventive lampapproximates the daylight curve with a correlated color temperature of5500 K.

Besides using the lamp of the present invention, due to its good colorrendering properties, for high quality color television live pickup andfor the lighting of stadiums and exhibition halls, the lamp is alsosuited, due to its daylight-resembling color, for all places whereillumination in addition to daylight is required.

Terbium also appears to be an element useful in the present invention.In the examples, holmium and/or thulium may be replaced by europium orlutetium.

. We claim:

l. A high pressure mercury vapor discharge lamp comprising a quartzglass discharge tube;

electrodes of refractory metal protruding into the discharge tube andspaced by a'distance which is a multiple of the discharge tube diameter;

an envelope surrounding the discharge tube; metal halides and an inertgas as additive fill to the mercury, contained in the discharge tube;

the improvement wherein the discharge tube contains halides of at leastthree elements which have essentially similar median excitation energy,and which comprise dysprosium and at least two other rare earth metals,said dysprosium and at least two other rare earth metals being presentin a total amount of from 0.3 to 1.2

mg/cm of arc length which during operation of the lamp provide asaturated vapor pressure and a wall loading of between 8 and 20 W/cm 2.Discharge lamp as set forth in claim 1, wherein the total amount of rareearth metals is between 0.5 and 0.9 mg/cm of arc length. 7

3. Discharge lamp as set forth in claim 1, wherein heat-accumulatingcoatings are provided at the end portions of the discharge tube.

4. Discharge lamp as set forth in claim 3, wherein the heat-accumulatingcoatings comprise ZrO- 5. Discharge lamp as set forth in claim 1,wherein the halides are iodides.

6. The discharge lamp as set fof'th in claim 1 wherein the dischargetube contains the halides of holmium and thulium in addition to that ofdysprosium.

7. The discharge lamp as set forth in claim 6 wherein the discharge tubealso contains the halide of erbium.

8. The discharge lamp as set forth in claim 6 wherein the discharge tubealso contains the halides of thallium and cesium.

9. Discharge lamp as set forth in claim 8, wherein the halides areiodides.

10. The discharge lamp as set forth in claim 1 wherein the dischargetube contains at least two of the halides of holmium, thulium, erbium,europrum, and lutetium, in addition to the halide of dysprosium.

11. The discharge lamp as set forth in claim 1 wherein the dischargetube contains the halide of at least one other element than the saidrare earth metals, said other element and said rare earth metals havingsimilar median excitation energy.

12. The discharge lamp as set forth in claim 1 wherein the dischargetube also contains the halides of thallium and cesium.

13. The discharge lamp as set forth in claim 12 wherein said halides areiodides.

1. A HIGH PRESSURE MERCURY VAPOR DISCHARGE LAMP COMPRISING A QUARTZGLASS DISCHARGE TUBE; ELECTRODES OF REFRACTORY METAL PROTRUDING INTO THEDISCHARGE TUBE AND SPACED BY A DISTANCE WHICH IS A MULTIPLE OF THEDISCHARGE TUBE DIAMETER; AN ENVELOPE SURROUNDING THE DISCHARGE TUBE;METAL HALIDES AND AN INERT GAS AS ADDITIVE FILL TO THE MERCURY,CONTAINED IN THE DISCHARGE TUBE; THE IMPROVEMENT WHEREIN THE DISCHARGETUBE CONTAINS HALIDES OF AT LEAST THREE ELEMENTS WHICH HAVE ESSENTIALLYSIMILAR MEDIAN EXCITATION ENERGY, AND WHICH COMPRISE DYSPROSIUM AND ATLEAST TWO OTHER RARE EARTH METLS, SAID DYSPROSIUM AND AT LEAST TWO OTHERRARE EARTH METALS BEING PRESENT IN A TOTAL AMOUNT OF FROM 0.3 TO 1.2MG/CM OF ARC LENGTH WHICH DURING OPERATION OF THE LAMP PROVIDE ASATURATED VAPOR PRESSURE AND A WALL LOADING OF BETWEEEN 8 AND 20 W/CM2.2. Discharge lamp as set forth in claim 1, wherein the total amount ofrare earth metals is between 0.5 and 0.9 mg/cm of arc length. 3.Discharge lamp as set forth in claim 1, wherein heat-accumulatingcoatings are provided at the end portions of the discharge tube. 4.Discharge lamp as set forth in claim 3, wherein the heat-accumulatingcoatings comprise ZrO2.
 5. Discharge lamp as set forth in claim 1,wherein the halides are iodides.
 6. The discharge lamp as set forth inclaim 1 wherein the discharge tube contains the halides of holmium andthulium in addition to that of dysprosium.
 7. The discharge lamp as setforth in claim 6 wherein the discharge tube also contains the halide oferbium.
 8. The discharge lamp as set forth in claim 6 wherein thedischarge tube also contains the halides of thallium and cesium. 9.Discharge lamp as set forth in claim 8, wherein the halides are iodides.10. The discharge lamp as set forth in claim 1 wherein the dischargetube contains at least two of the halides of holmium, thulium, erbium,europrum, and lutetium, in addition to the halide of dysprosium.
 11. Thedischarge lamp as set forth in claim 1 wherein the discharge tubecontains the halide of at least one other element than the said rareearth metals, said other element and said rare earth metals havingsimilar median excitation energy.
 12. The discharge lamp as set forth inclaim 1 wherein the discharge tube also contains the halides of thalliumand cesium.
 13. The discharge lamp as set forth in claim 12 wherein saidhalides are iodides.